Category: Lighting

Some problems best solved outside the visible spectrum

Most of us think about vision with a human bias, since most of us are normally sighted with color stereo vision. We perceive distance, hues, shading, and intensity, for materials that emit or reflect light in the wavelengths 380 – 750 nm. Many machine vision problems can also be solved using monochrome or color light and sensors in the visible spectrum.

Many applications are best solved or even only solved, in wavelengths that we cannot see with our own eyes. There are sensors that react to wavelengths in these other parts of the spectrum. Particularly interesting are short wave infrared (SWIR) and ultraviolet (UV). In this blog we focus on SWIR, with wavelengths in the range 0.9 – 1.7um.

Examples in SWIR space

Food processing and agricultural applications possible with SWIR. Consider the above images, where the visible image shows what appears to be a ripe apple in good condition. With SWIR imaging, a significant bruise is visible – as SWIR detects higher densities of water which render as black or dark grey. Supplier yields determine profits, losses, and reputations. Apple suppliers benefit by automated sorting of apples that will travel to grocery shelves vs. lightly bruised fruit that can be profitably juiced or sauced.

Whether controlling the filling apparatus or quality controlling the nominally filled bottles, SWIR light and sensors can see through glass or opaque plastic bottles and render fluids dark while air renders white. The detection side of the application is solved!

Hyperspectral imaging

Yet another SWIR application is hyperspectral imaging. By identifying the spectral signature of every pixel in a scene, we can use light to discern the unique profile of substances. This in turn can identify the substance and permit object identification or process detection. Consider also multi-spectral imaging, an efficient sub-mode of hyperspectral imaging that only looks for certain bands sufficient to discern “all that’s needed”.

How to do SWIR imaging

The SWIR images shown above are pseudo-images, where pixel values in the SWIR spectrum have been re-mapped into the visible spectrum along grey levels. But that’s just to help our understanding, as an automated machine vision application doesn’t need to show an image to a human operator.

In machine vision, an algorithm on the host PC interprets the pixel values to identify features and make actionable determinations. Such as “move apple to juicer” or “continue filling bottle”.

Components for SWIR imaging

SWIR sensors and cameras; SWIR lighting, and SWIR lenses. For cameras and sensors, consider Allied Vision’s Goldeye series:

Goldeye SWIR cameras are available in compact, rugged, industrial models, or as advanced scientific versions. The former has optional thermal electric cooling (TEC), while the latter is only available in cooled versions.

For SWIR lighting, consider Effilux bar and ring lights. Effilux lights come in various wavelengths for both the visible and SWIR applications. Contact us to discuss SWIR lighting options.

By emitting light in the SWIR range, directed to reflect off targets known to reveal features in the SWIR spectrum, one builds the components necessary for a successful application.

And don’t forget the lens. One may also need a SWIR-specific lens, or a hybrid machine vision lens that passes both visible and SWIR wavelengths. Consider Computar VISWIR Lite Series Lenses or their VISWIR Hyper-APO Series Lenses. It’s beyond the scope of this short blog to go into SWIR lensing. Read our recent blog on Wide Band SWIR Lensing and Applications or speak with your lensing professional to be sure you get the right lens.

Takeaway

Whether SWIR or UV (more on that another time), the key point is that some machine vision problems are best solved outside the human visible portions of the spectrum. While there are innovative users and manufacturers continuing to push the boundaries – these areas are sufficiently mature that solutions are predictably creatable. Think beyond the visible constraints!

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1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera and components selection.  With a large portfolio of lenses, cables, NIC cards and industrial computers, we can provide a full vision solution!

In this article we discuss when and why one might want to strobe a light instead of using continuous lighting. While strobing traditionally required a dedicated controller, we go on to introduce that CCS and AVT have published an Application Note showing how the Allied Vision Mako camera can serve as the controller!

While LED lights are often used for continuous lighting, since that’s an easy mode of deployment, sometimes an application is best served with a well-timed strobe effect. This might be for one or more of the following reasons:

• to “freeze motion” via light timing rather than shutter control alone;
• to avoid the heat buildup from continuously-on lights
• overwhelm ambient lighting
• maximize lamp lifetime

Let’s suppose you’ve already decided that you require strobe lighting in your application. You’re past “whether” and on to “how to”.

Since you are moving into the realm tight timing tolerances, it’s clear that the following are going to need to be coordinated and controlled:

• the strobe light start and stop timing, possibly including any ramp-up delays to full intensity
• the camera shutter or exposure timing, including any signal delays to start and stop
• possibly the physical position of real world objects or actuators or sensors detecting these

Traditionally, one used and external controller, an additional device, to control both the camera and the lighting. It’s a dedicated device that can be programmed to manage the logical control signals and the appropriate power, in the sequence required. This remains a common approach today – buy the right controller and configure it all, tuning parameters through calculations and empirical testing.

Call us if you want help designing your application and choosing a controller matched to your camera and lighting requirements.

But wait! Sometimes, thanks to feature-rich lighting equipment and cameras, with the right set of input/output (I/O) connections, and corresponding firmware-supported functionality, one can achieve the necessary control – without a separate controller. That’s attractive if it can reduce the number of components one needs to purchase. Even better, it can reduce the number of manuals one has to read, the number of cables to connect, and the overall complexity of the application.

Let’s look at examples of “controller free” applications, or more accurately, cameras and lights that can effect the necessary controls – without a separate device.

Consider the following timing diagram, which shows the behavior of the Effi-Ring when used in auto-strobe mode. That doesn’t mean it strobes randomly at times of its own choosing! Rather it means that when triggered, it strobes at 300% of continuous intensity until the trigger pulse falls low again, OR 2 seconds elapse, whichever comes first. Then if steps down to continuous mode at 100% intensity. This “2 seconds max” feature, far longer than most strobed applications require, is a design feature to prevent overheating.

OK, cool. So where to obtain that nice square wave trigger pulse? Well, one could use a controller as discussed above. But in the illustration below, where’s the controller?!? All we see are the host computer, an Allied Vision Mako GigE Vision camera, an Effilux LED, a power supply, and some cabling.

How is this achieved without a controller? In this example, the AVT Mako camera and the Effilux light are “smart enough” to create the necessary control. While neither device is “smart” in the sense of so-called smart cameras that eliminate the host computer for certain imaging tasks, the Mako is equipped with opto-isolated general purpose input output (GPIO) connections. These GPIOs are programmable along with many other camera features such as shutter (exposure), gain, binning, and so forth. By knowing the desired relationship between start of exposure, start of lighting, and end of exposure, and the status signals generated for such events, one can configure the camera to provide the trigger pulse to the light, so that both are in perfect synchronization.

Note: During application implementation, it can be helpful to use an oscilloscope to monitor and tune the timing and duration of the triggers and status signals.

Whether your particular application is best served with a controller, or with a camera that doubles as a controller, depends on the application and camera options available. 1stVision carries a wide range of Effilux LED lights in bar, ring, backlight, and dome configurations, together with the ability to be used on continuous or strobe modes.

1st Vision’s sales engineers have over 100 years of combined experience to assist in your camera and components selection.  With a large portfolio of lenses, cables, NIC card and industrial computers, we can provide a full vision solution!